Infants were randomly assigned to receive either INH or placebo by mouth daily, beginning between the 91st and 120th day of life, and at least 90 days after Bacille Calmette-Guerin (BCG) vaccination. At sites in South Africa, HIV-infected infants received daily trimethoprim/sulfamethoxazole (TMP/SMX) as Pneumocystis jiroveci pneumonia (PCP) prophylaxis until at least 1 year of age; HIV-uninfected infants received TMP/SMX until at least 6 months of age.